text:
What is the equation for calculating static thrust?
I'm building a quadcopter as my bachelor's degree thesis. I'm having trouble finding a reliable equation for calculating the static thrust for a quadcopter. The equations I have found give me ridiculous results. I know that it's difficult to derive such an equation and I know that there are online calculators (like this). But how do these calculators calculate static thrust? There has to be an approximate equation somewhere. This is what I'm asking. I don't mind the equation(s) that lead me to there, I would just like to know them.
Edit: More information
The following snapshot is taken from Mathcad software. It's various equations i have gathered from supposed trustworthy websites. These equations lead me to the calculation of static thrust. I think the equations are pretty self explanatory. Thank you.

Components of the quadcopter: Battery, ESC's, Motors, Propellers, frame
Various useful websites that i've found most equations: 1, 2, 3, 4

Please show what you have - in the end, we will give you the equations which do not work for you. You would also post sample code in a question on SE, right?

I have added more information. Thank you.

Did you check your units? Quadcopter with 3 meter diameter rotors?

Thanks. It seems i've made some careless mistakes. 3 is in inches and one equation is supposed to be in inches but the other is in meters. I've also made a mistake with the RPM. I will correct them all and let you know soon.

No the RPM wasn't in thousands. Forget that. I have uploaded a new picture after applying various fixes. Things now have definitely improved. Still though that 15 kilograms in the end is A LOT. In essence since the quadcopter's weight is 500kg, i've found from another equation that the total thrust generated should be from 2 to 3 times the weight of the quadcopter. So between 1 and 1.5 kilos. So there must be further improvements to be made. I've also added links to the critical components of the quadcopter and various useful websites in which i've found most of these equations.

Instead of updating a picture, why don't you post the equations? (if you do not know how to use mathjax we can edit them for you afterwards)
Also, use metric units off the bat, it will save you a lot of headaches.

I know mathjax, but in this case there are a lot of equations so i thought a picture would be alright. Thank you.

By now you should have found this answer on static thrust. It explains how to arrive at this equation for static thrust $T_0$:
 $$T_0 = \sqrt[3]{P^2\cdot\eta_{Prop}^2\cdot\eta_{el}^2\cdot\pi\cdot \frac{d_P^2}{2}\cdot\rho}$$
Your P is at most 11.1 V × 4.5 A = 49.95 W. Your prop efficiency $\eta_{Prop}$ must be guessed; let's take 60%. The electric efficiency should be higher; let's use 95% for now. The prop diameter $d_P$ is 3 or 5 inches (depends if your comments or the picture in your question is more reliable), so I use 0.127 m for now. Air density is given with 1.18 kg/m³.
When I plug in the numbers, I get 2.894 N. One propeller can lift approximately 295 g of quadcopter, and all four will produce thrust equivalent to the weight of 1.18 kg in Earth's gravitation. Looks about right for a quadcopter of 500 g.
Don't assume that the motor delivers all the power the propeller can absorb. Also, don't assume that the RPM of the isolated motor can be maintained when it is driving a propeller.

Your answer made me look a lot more into the theory of aviation and try to understand more about all these concepts. I realized i didn't even know the basics. Also this SE website helped me a lot in very little time, in finding answers to my questions. Of course, i'm only getting started. Thank you very, very much!

@RestlessC0bra: You best thank me by contributing back, and you did already. I reworked the numbers, and now they should be even more right.

I believe it should be a square root instead of the cube root (the same mistake is in the original answer as well). It's a nice approximation, however, I think $\eta_{Prop}$ is a function of wind speed so you should be sure to use an appropriate value.

@Chris: I don't think so. Please look at the original answer: The thrust is on the left side and in a square root on the right. First you need to square both sides and then bring thrust over to the left. This gives you an expression for thrust cubed. I know I made mistakes in other answers but try to correct them as much as I can. Please prove me wrong!

@PeterKämpf Yes, you are right I missed the $T_0$ under the square root. Sorry about that.

@PeterKämpf  Your answer looks great in the beginning but I am puzzled by one scenario after I've been thinking for last few days.
The equation assume the propeller is moving air.
If I use a propeller with zero pitch, or another word, zero angle of attack.
The propeller has an asymmetrical airfoil, so it still generates lift/thrust without moving the air. (Maybe a little, not much)
Does your equation still apply?

@mikewen An asymmetrical airfoil has camber. This gives it already some lift at zero angle of attack. Pitch, therefore, should be relative to the zero-lift angle.

@PeterKämpf Right, my question is that air is not moving at zero angle of attack.
But there are still lift/thrust due to the pressure difference.
So the fundamental of the above equation (mass of air that moved) does not apply?
Should I move the question to the original answer?

@mikewen I don't quite get what you are thinking. Without lift there is also no pressure difference, so no movement of air except for a centrifuge effect due to friction. Better write a question of your own!

There are a couple of examples on this site now (here and here for instance) for static propeller thrust calculation, based on existing considerations for helicopter hover. The theory can be found in books like Principles of Helicopter Aerodynamics by J. Gordon Leishman; Helicopter Performance, Stability, and Control by Raymond Prouty. The books start their explanations based on impulse theory for lifting disks, then expand with Blade Element Theory for a comprehensive explanation of rotating thrust blades.
The theory presented in the books is generally for open rotors, in Leishman there is some impulse based discussion on influence of ducting. Also, measurement based data in small ducted rotors in a masters thesis here.
All above is for relatively open rotors, with a low solidity ratio, up to 0.1. If power is not the limiting factor but diameter is, a fan with a solidity ratio of close to 1 as found here can be used, and scaled up or down according to blade area.


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Where can I find GA VFR maps for Australia?
Are there any sites similar to SkyVector (US-based) for GA aviation maps in Australia?
I understand that Air Services Australia has miscellaneous single-purposes maps available, but they seem to be mostly airport diagrams and approach procedures. I'm looking for GA VFR maps.
If the only thing available is SkyVector's world maps (of Australia), how accurate are they?

What do you mean by 'how accurate are they?'  Are you just looking for ones at a closer scale?

@Aaron I know that SkyVector is a US-based site. I know that their US-based charts are based on those freely released by the FAA. So I'm not sure whether the charts for Australia contain all pertinent information. Contrast all of the messages on something like a US-based TAC (e.g. for KSFO http://skyvector.com/?ll=37.62660124224426,-122.36052705916343&chart=127&zoom=1&plan=A.K2.KSFO) vs what's available in the most-zoomed-in section for YMML (Melbourne Airport) http://skyvector.com/?ll=-37.77303052079124,144.96514891430678&chart=301&zoom=1  -- There just seems to be much less information.

So I don't think you're looking for more accuracy (if I may be pedantic) but for more detail.  I think it depends on the provider.  FAA has TACs for all of their covered airspace that are available for digital download at very reasonable prices, and they also sell World VFR charts, which is what skyvector gives you when there's no sectional or TAC.  I'm not sure any other providers have as reasonable prices (or even digital versions)

So as you've noted, yes, Airservices Australia charges for their charts. So I was wondering whether, perhaps, if skyvector uses these as a basis for their Australia maps, if they don't update them as regularly as whatever the Airservices update cycle is, the they may be come outdated (and thus inaccurate). Speculation, but still possible.

So generally VFR charts don't get all that inaccurate with time (the earth doesn't move all that much). However the World VFR charts are a "product" from the FAA so they're accurate for some measure of accuracy. I'm not sure how the changeable information (runway length, frequencies, towers etc) is promulgated to the FAA but Air Services Australia seems to believe that someone owes them money for gathering all this information...

I have both US and Australian PPLs, and having flown VFR in both countries, there are some real differences in the VFR charts and supplemental data available. Mostly the contents are fairly evident but if you are unfamiliar with a specific type of VFR chart, it is important to look over the chart in detail to make sure you understand it.
The US publishes VFR charts known as Sectionals. These cover the entire country, including non-continental areas like Hawaii. IMHO these are excellent although in busy airspace, the 1:500,000 scale can become complex. So pilots learning to fly in the US usually become familiar with the sectional covering their base field, and then with that understanding, can look at sectionals for anywhere else in the US.
Printed sectionals can also be used for long range VFR flight planning as they can be laid out in sequence and routes plotted across adjoining chart boundaries. For online chart examination, SkyVector publishes all US sectionals online, which is a great resource.
Australia does not publish sectionals covering the whole country. It's a good question as to why but essentially the centre of the country is a big desert where few people live. So from a historical perspective, the inner part of the country has been regarded as "remote" and thus less in need of highly detailed maps. In addition, the word 'sectional' isn't even in Australian pilot lexicon, so use the word 'chart' instead.
Australia publishes Visual Terminal Charts (VTC) for each large metropolitan area which are a Mercator projection at 1:250,000. And there are Visual Navigational Charts (VNC) which mostly encapsulate the VTCs and are at 1:500,000 (same as sectionals). The image below is an example of the Brisbane VTC.

As VTC/VNCs cover only largely populated areas, for printed chart long VFR route planning, you will need to revert to the World Aeronautical Charts (WACs), pronounced 'whacks'.

WACs started as an ICAO project after WW2 to transition from the existing US-based international wartime series and so all Allied nations were effectively asked to harmonize their maps with a US design. But in 2015, the FAA stopped WAC production and thus a recently US-trained VFR PPL would never have heard of them(!)
The US WAC coverage looked like this:

WACs are a Lambert projection at 1:1,000,000 and in Australia, printed chart VFR route planning would be done over sequential WAC's, with likely a supplemental VNC chart for the populated areas to be crossed. WAC's do not contain airspace (although supposedly an aeronautical chart!). They are essentially a topo map with features that are easy to spot from the air.

So, to answer the OP's question - no, there are no free online sources for Australian government produced charts. SkyVector shows a very data sparse US Sectional-like view of Australia but I wouldn't use it for anything other than simple distance/leg planning.
However, all of the previously mentioned chart types for Australia are now encapsulated and adjoined in a single app known as OzRunways. I have no association with them, other than being a customer. Another answer has also referred to this as well.
OzRunways works on both iOS and Android and in my experience seems very widely used amongst Australian VFR pilots. For VFR use, they provide a so-called 'Hybrid VFR Map' which simply uses the most detailed chart available. Price at time of writing is about AUD $100 and chart-wise also has New Zealand and Papua New Guinea.
But also of value to pilots flying in Australia, there is comprehensive airfield information available in the ERSA (EnRoute Supplement Australia), which is a free download. It lists technical aspects/refueling contacts/etc. for every sizeable airfield in Australia. In addition to this, AOPA also publish a pilot guide for various airfields. OzRunways contains the ERSA and for an extra amount, they also will bundle the pilot's guide.
I would value any other comments about VFR chart sources for Australia but hopefully this is a good overview.

What an excellent, detailed answer. You might want to mention US Terminal Area Charts in your discussion of US complex airspace for a fair comparison.

Nice answer but why did you write that there are no free online sources for Australian government produced charts. It seems to me that airservices does indeed make the VTC and VNC available free of charge under the AIP Charts section of their website. Did I misunderstand your sentence?

@VH-NZZ is right, I am looking at some of the AU VTC and VNC charts right now. To get them, go to the Aeronautical Information Package page, click the "I Agree" button at the bottom, and then find the AIP Charts link on the next page. Could you update the answer to reflect this?

Airservices Australia now publishes electronic versions for free. Use requires acceptance of an agreement. Access as follows:

Click Publications on the Air Services Australia website.
Click Aeronautical Information Products – (AIP) at the top.
Accept the agreement
Select an AIP Charts option on the subsequent page.

Flyermaps provides Australian VFR charts.

I believe OzRunways.com have a VFR package, but it seems to be just for i-devices at the moment.

+1. I did a search for the CAR 233(1)(h) but couldn't find any other providers advertising this. Seems to be the only one.

Australia only produces 1:1,000,000 WAC charts for the whole country.  The more detailed 1:500,000 VNC charts like we have in Canada are available only around major cities.  The VNC chart is similar to the US "sectional" chart.  VNCs are available from Air Services Australia, the state-owned entity responsible for airspace management and aeronautical information.

@DanHulme Unfortunately, I think in Australia that Air Services Australia might be the main/official provider of such charts. So I don't think it's link spam. Per their website: "Airservices is a government owned organisation providing safe, secure, efficient and environmentally responsible services to the aviation industry." So +1 from me for the post.

Disagree with all the down-votes here. Jeppeson has been linked before and at least airservices is gov't owned. +1 from me.

@CJBS That's right. That link wasn't the link in the answer when I posted that comment. Mr Burke is a new user and I think he now understands what's expected of answers.

@CGCampbell the link was editted by voretaq. Also i expect link post in answer to be the link to the answer. Otherwise when us regulation question comes up you will see lots of faa.gov link.

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Does a system exist that can bulk process satellite data to find a plane lost over ocean?
The case of the lost Malaysian Airlines plane is tragic for all those involved.
In the case of such a plane lost over the ocean, hypothetically (and described very simplistically), it would seem that the fastest way to search for wreckage would be:

to define an area to be searched
wait for the latest satellite images for that area at high-resolution to be available (given appropriate positioning and programming of the satellites)
then search the captured imagery for deviations from ocean blue

Presumably this could be done reasonably quickly by a computer, and that satellite imagery is taken after a suspected crash, and exceptions (e.g. spots of white amongst the blue) are able to be verified by a human.
Does such a system exist? Are imaging satellites able to be configured to take such imagery on demand over a large area? And do such batch-image processing systems exist for this purpose?

Update: Satellites were eventually used in the search for MA370, see this article.

This question might be better answered by the folks at space exploration but here's a shot:

Oil slicks are not uncommon at sea, so finding one from the aircraft is not too easy.
It's an incredibly large area pulling a lot of processing power. You're going to need pretty good resolution imagery over several square kilometers and then run image recognition on it. Look at this image which has a scale of 25 miles which is still a fraction of what you would need to get an idea:

The fragments you're looking for are very small in regards to waves. I suspect depending on where you are there's a large amount of noise from other rubbish which is hard to filter out, such as a white plastic sheet to a door. You might even go confusing big aircraft parts to other white boats. Yes, you can continue the search but it takes time to go through all of these and dismiss them.
A lot of volunteers searched for Steve Fossett when he went missing, and there was some attempts to locate him by satellite imagery from google maps, which was not successful.
Aircraft, while not fast, can be over the side within a few hours, while I think you have to wait until the satellites have caught all the imagery you would like.

While I think it could be done as you say, you would need to develop software and I don't think the market for it exists, but that's just my guess. Reading up it appears that satellites are used against drug cartels along the USA-Mexico border and against illegal immigrants elsewhere in the world.

Note that, in general, searching Google Maps won't help because the "satellite" (actually, mostly aerial) imagery is often several years out of date. In the Fossett case, Google obtained fresh imagery from Digital Globe

My point with the satellites was that for government satellites, compared with the cost of sending government-paid search/recovery efforts, especially with military resources, there might be a cost advantage to temporarily re-purposing satellites to capture data over a given area. The data obtained by Google is only updated infrequently, but satellite data can be updated within one or two days in some cases.

The point about wave/wash colour in comparison to mostly white aircraft parts is a good one.

Another attempt to use satellite imagery in the search.

@CJBS the main problem with repositioning satellites for spot use like this is that they only have a limited amount of fuel for doing that, and that's needed to keep the satellite in a stable orbit as well. Thus repositioning it for the purpose of taking a few snapshots of a patch of open ocean is extremely costly, it reduces the life of that satellite by potentially years, which given the construction and launch cost means a price tag of tens of millions of dollars. Cheaper to fly out a P3 or other patrol aircraft.

Massive area, large search interval, no complete coverage of the entire area, especially no permanent coverage of the entire area, weather, limited computer power.
All those factors, each on their own, would make the problem massive. Taken together they make it insurmountable.
We're talking an area of several million square kilometers that needs to be searched, at a resolution of a few square meters, over an interval of several hours.

Not only is there no 24/7 photographic coverage at that resolution available of any spot on the planet, it certainly won't exist of a stretch of open ocean in a backwater of geopolitical interest (it MIGHT exist just around the time of a drone strike on a Taliban compound for example, over an area of a few hundred meter around that compound, for maybe 10 minutes prior to 10 minutes past, but that data would be highly classified for obvious reasons and utterly useless unless an airliner crashed right on top of that compound during that small window).

Manfred hints that satellite coverage is used against drugs and human trafficking and it may be. But it can't detect individual human beings. It CAN potentially detect patterns, like finding paths through brushland that from the ground can't be easily seen but from the air show up. And in case of anti-trafficking use, it mainly is used to surveil known or suspected points of departure, say an airfield in Colombia known to be used by drugs smugglers, and alert law enforcement agencies of a possible inbound aircraft which can then be tracked using other means (like AWACS) and intercepted. Same with boats. But it's not real time, it's photos taken at several hour intervals of known "points of interest".

We simply lack the resolution to see something the size of a human being (or a floating piece of aircraft debris like a toilet seat or life jacket) from orbit.

Oil slicks, which tend to spread out a lot, can be observed and investigators sent to the area. This is used in coastal regions to find and fine ships that illegally dump oil from their balast tanks. But again, there's no permanent coverage and certainly not over open ocean. Maybe some country with the capability can redirect one of its satellites after the suspected crash, and hopefully when it gets there it's not too late (dispersal is rapid) AND the weather is clear AND there's daylight AND everything else falls into place.

No, the best hope is narrowing down the area based on last radio or radar reporting position, and do an area search from there. And if you get real lucky you get a responder in the FDR or CVR to give you a beep, or an emergency beacon in a life raft that got shook loose and turned itself. Other than that, fingers crossed that someone with a pair of binoculars spots something floating out there before it's all sunk to the bottom.

I don't think satellites can be used against drug trafficking. They are used against drug production, because coca plantations can be recognized by colour on a multi-spectral satellite image. Plus they can show paths even (to an extent) under tree cover, giving away locations of hidden facilities. They can show jungle airports as they are larger deforested patches, but they can't catch a suspicious plane. Radar or AWACS is needed for that.

I would have thought that, even for an aircraft that collides with the ocean in-tact, wouldn't a signal have been transmitted from its 406 MHz ELT following the impact? Presumably at least some of the wreckage floats for a brief period before sinking. 406 MHz ELTs transmit to satellites. Of course this is assuming that the tail of the plane doesn't go underwater immediately and continue to sink without a chance to transmit a clear signal first.

@JanHudec they're used to help in interdicting large shipments through surveillance of known shipping routes. They can't of course detect whether an aircraft has drugs in it, but they can detect an unscheduled departure for example by IR imaging of airfields.

Digital Globe, a satellite imaging company (who provide a lot of the data Google uses), has done this for the MH370 flight using a platform called Tomnod, which is currently directing all users straight to the search page. The images they're showing now were taken on 3/9, so apparently they are able to re-task their satellites fairly quickly.
More info on how to use this is available at How To Use Tomnod To Find MH370.
Something similar was done using Amazon Mechanical Turk during the search for Jim Gray.

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How does aircraft design affect carburetor ice?
The Cessna 172 and Piper Warrior are similar in many ways, including their engines: for most of their production history (1968-1998 for the 172; the entire history for the Warrior) both were equipped with a Lycoming O-320 engine of 150 or 160 horsepower.
One significant difference between the two is in their before-landing checklists: the 172 instructs the pilot to turn carburetor heat on before closing the throttle (p. 4-19):

Carburetor heat should be applied prior to any significant reduction or closing of the throttle.

Conversely, the Warrior recommends carburetor heat "if required", and even recommends against it unless necessary (p. 4-23):

Carburetor heat should not be applied unless there is an indication of carburetor icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburetor heat on can cause detonation.

Considering that these two aircraft have very similar engines, what would explain such a drastically different approach to the potential danger of carburetor icing?

"Full throttle operation with carburetor heat on can cause detonation." Woah! Does that mean what it looks like?

@raptortech97 Maybe you should ask about it ;-)

@raptortech97 "Detonation" in an engine context doesn't always mean a catastrophic explosion: the term can also refer to "knock", where the mixture explodes prematurely or too suddenly, making the engine shudder and probably operate at low power. Not sure if it means that in this case.

Still doesn't make a ton of sense since carb heat makes the mixture richer, cooling the engine, while detonation usually refers to incorrect ignition to to hot points in the engine.

I've downvoted the answer from Habu because it ignores a major difference in engine design.
For small GA planes, the Lycoming engines have the carburetor bolted to the bottom of the crankcase where it gets some heat from the hot oil.  Fuel/air exits the top of the carb where it is routed through pipes inside the crankcase where the hot oil further increases its temperature. This makes the Lyc generally resistant to induction icing.
In Continentals, the updraft carburetor is not mounted on the hot crankcase but on part of the manifold assembly, insulating the carb itself from the heat of the crankcase, and the fuel/air mixture is routed directly to the intake manifold and not through the engine crankcase which holds the hot oil.  The result is that the TCM O-300 engine has earned the reputation of being an icemaker. The difference in the POH instructions as to how to fly each engine is directly attributable to engine design and it has absolutely nothing to do with the weather in Vero Beach versus Wichita.
I'm going to post line drawing images of the two engines to illustrate the point. First: Lycoming.  Second: Continental
What the original poster is missing is that for most of its history, the Cessna design used Continental engines.  Now that it has switched to Lycoming engines, the difference in the engines is probably zero, but they have not abandoned the former POH instructions as that might be confusing to the pilots that fly these planes.  After all, using carb heat more often as a default procedure for the Lyc powered Cessnas is a safe procedure.

I stand corrected. I was unaware that early model Skyhawks came with that particular engine configuration. Taking my answer down to avoid further confusion.

I knew this was the answer, and I tried to find photos and an authoritative source, but I didn't have enough time. Good on ya.

Carby heat should be used on final (and any other significant idle or near idle descent) until you reach around 300 fleet AGL to prevent icing. It should then be turned off during the final part of your approach so that you'll have full power available in case you need to execute a go around.
I think what you've found is not a difference in engine design, but a difference in wording in the respective manuals. The Cessna handbook states that heat should be applied during any significant closing of throttle, which is correct (as presumably you'll also be descending shortly after closing throttle), but it should also be turned off prior to touching down in case you need to rapidly apply full throttle for go around, as per the Warrior manual.


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Is a VOR check required to legally fly an ILS approach under IFR?
The FARs require a check of the VOR receiver before IFR flight:

§91.171 VOR equipment check for IFR operations.
(a) No person may operate a civil aircraft under IFR using the VOR system of radio navigation unless the VOR equipment of that aircraft

...has been checked using a procedure described immediately following.
Does this apply to an ILS approach? Specifically, consider a flight conducted entirely using GPS, except that it terminates in an ILS approach. In most (or all?) aircraft, the ILS and VOR receivers are one and the same. However, the mechanism of how an ILS and VOR work are very different.
The FARs speak of "the VOR system of radio naviation". Is that specifically for actual VORs, or does it encompass the ILS by virtue of being the same receiver and CDI?

Really good question - my instinct would have been to say "yes of course". Thanks to this question and @digitgopher's answer I've learned something today.

This regulation does not apply to an ILS approach.
You are right is saying that "the VOR system of radio navigation" refers to actual VORs.
If the flight is conducted using GPS to an ILS approach then you aren't using VOR for navigation. It does not matter that ILS uses the same instrument display.
Intuitively, though ILS and VOR use the same display and frequency band, they are functionally different. The VOR beacon sends out a omnidirectional signal, from which a bearing (0-359 degrees) is calculated. The ILS sends out a focused, directional signal, which the receiver centers on.

The VOR receiver check is verifying that the needle can interpret the correct radial within a specified tolerance.
It appears you know how the two separate systems work so a bad VOR check won't affect the accuracy of the localizer system.  Hence, there is no regulation prohibiting it.


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How much simulator training for general-aviation?
How much training/refreshing is necessary/desirable for instructing general aviation pilots? All I see is commercial pilots been trained in simulators.
A real general aviation airplane might be not much more expensive than a realistic flight simulator (full-motion  simulators with hydraulics), but wouldn't training specific scenarios (like engines-off, bad weather) in a simulator be a significant enhancement in their education?

There are a lot of simulators out there for those uses. My flight school used to have a Redbird simulator that I think cost on the scale of $75,000 and had 2 degrees of freedom. There are more basic ones too that can be used for training, like the Redbird Jay and other cheaper ones that can be certified for some training scenarios.

Zero simulator time is necessary, pilots have been trained for decades without them and the stats show they are reasonably safe. Whether they can be made even safer via sims is a matter of opinion, and I can think of a few arguments against it.

Does this answer your question? Can Microsoft Flight Simulator help me learn to fly (or make me a better pilot)?

@Pondlife: I meant a real professional flight sim, no improvised solutions.

Under FAA rules, simulator training is not a requirement for any certificate/license. Only a certain amount of simulator training can be substituted for training in an actual aircraft for each certificate. Even then, only simulators certified by the FAA can be counted towards training time. The cost of the hardware and complexity of the software necessary to be good enough to receive FAA certification makes only high level FFS devices financially advantageous for airlines. These devices compared to the average home simulators is like the difference between 1970s TV night to holographic day.
Then, the question is if the allowed simulator time makes sense for the General Aviation pilot. Part 61.109 allows 2.5 hours of sim time to be substituted for actual flight time towards a private pilot certificate. That number doubles if the training is done in a Part 142 training center. By the time you get to the 1500 hours required for an ATP, ...

Not more than 100 hours of the total aeronautical experience requirements of paragraph (a) of this section or §61.160 may be obtained in a full flight simulator or flight training device provided the device represents an airplane and the aeronautical experience was accomplished as part of an approved training course in parts 121, 135, 141, or 142 of this chapter.

If the time requirements for aeronautical experience were arbitrary to the need for training, a flight simulator can be a viable option. A realistic AATD (Advanced Aviation Training Device) would be affordable for a General Aviation flight school.  Compared to the millions of dollars of a full-motion FFS (Full Flight Simulator), an AATD would be less than $100,000. Most flight schools in my area would charge a student roughly half the hourly rate for an AATD that they would for the typical 4-seat, 6-pack, single-engine, fixed-winged trainer aircraft.
Unfortunately, the lack of realism in an AATD makes it a valuable tool for procedures training only. An AATD lacks the feel and feedback of real flight. Its value is only as good as the student, instructor, or pilot’s diligence to following the procedures. To gain the most training benefit from an AATD carry out the flight using flight planning, flow checks and checklists to their fullest. Role-playing ATC will further add to this benefit. Treat it like a real flight and not like a game.
Anecdotally, I have trained on sims ranging from full-motion Redbird BATDs with custom G1000 bezels to stationary AATDs with fully functional instruments and controls, home sims on personal computers to multimillion dollar full-motion, gimbaled FFSs at the American Airlines Training Center. Except for the AATC FFS, none of them had the realistic force feedback of a real flight. None but the FFS had software sophisticated enough to mimic landings or wind interaction with enough realism. And, the FFSs are far too expensive for general aviation use. Actual flight time in a GA trainer aircraft would be cheaper.

@FreeMan - Good catch. That should have read “None but the FFS had software sophisticated enough to mimic landings or wind interaction with enough realism.”

Whew! Had me worried...

I am strongly in support of silmulator training, especially for a person going through a part 61 program.  My personal experience so far is that you put up a small fortune to learn this stuff, you really want to get the most out of it that you can so that you can be a solid and confident pilot.  Everyone learns differently, but in my case I seem to be having an easier time with the physical aspects of controlling the plane and a harder time with the atc communications and just the overwhelming amount of information that you need to learn, even for basic proficitiency to become a private pilot.  There are many aspects of flying that are situational and relient on just plain judgement which can certainly be reinforced with time in a simulator.
When I get done with a session with my ninja instructor, the first thing I do is brain dump my memmories into an apple notes file.  Proceedures, speeds, timing items. Questions.  Anything that you will need to remember from here on out.  Aythong thing that you know, you don’t know. :)
Take the things that are confusing and see if you can learn them in a simulated env.  Maybe so, maybe not. I realized that I really don’t understand many aspects of cross counrty flights..  so then you start to figure out how to reads docs and charts to get the most relevet info. It's really a pursuit of knowlege.. you need to employ tools at your disposal to get there.
I firmly believe that sims (I’m using x-plane 11 on a mac) are invaluble as an addition to real flight training.  When you are paying for the instructor, and the plane, and the fuel... the time flies by. The sim alows you to just take a breath and think about all the things that your ninja instructor said durring your last 2 hour session. Look in your notes and try to recreate the items that were confusing in the real flight.

Simulator training takes a lot of forms; from actual simulators that replicate the cockpit and characteristics and systems of an actual airplane, to simple devices that represent the general concept of an aircraft.  They're used for instrument procedures trainers, as well as a much less expensive version of large, sophisticated aircraft. It's a lot less expensive to train for two months in a simulator, than the actual airplane.
That said, there are a number of general aviation simulators, from light singles and twins to corporate jets.  Even the Air Tractor 802 has a simulator.
Competent simulator-based training can be very effective, and is sometimes mandated by insurance providers.
There's a reason that the general aviation mishap rate is considerably higher than professional commercial aviation, and it's not a matter of flight hours of experience.  A lot of it comes down to standardization and training.

There is no requirement for flight simulator training in general aviation as far as I'm aware but you can save a ton of money during flight training if you use flight simulators. A basic setup could be cheaper than one flight hour and depending on the aircraft you are training for it could save you thousands of dollars/euros in the long run. Even chair flying (literally sitting on a chair and pretending to fly) can re-enforce patterns and reduce training costs.
Commercial pilots are training in flight simulators for that exact reason: it's much cheaper than practicing with an actual aircraft. Some of the situations they train for are just too risky to perform in real life. And also you can't just wait for the weather to turn bad to do the exercise.
In my opinion a flight simulator on a normal desktop PC with a good set of hardware input devices i.e. a yoke or stick and a pair of rudder pedals as well as a throttle quadrant, already provides 90% of the training that a much more expensive motion simulator can offer. On the other hand you can replace real world flight hours with a fully professional sim which you can't do with a home PC flight sim.
A friend of mine recently started his helicopter flight lessons and practiced for about 20 to 30 hours before his first flight with an instructor. In the first lesson after a few minutes he was already able hover on his own and therefor skipped ahead about three or four flight lessons. That saved him a ton of money and also gave him much more confidence and took away a lot of the stress and he was really enjoying the flight training from that point forward.
If you're looking to start flight training I'd recommend practicing the first steps within the safe environment of a flight simulator with online tutorials or videos or even better with the help of a friend who already flies or a flight instructor. When you reach between 30 to 100 hours of home flight simulator time and manage to not crash all the time and make the first good landings then you should seek the expertise of an actual flight instructor before you enforce bad habits. Once you have started flight training you can repeat the flight lessons at home to try and perfect your skills. I'm sure your flight instructor will be blown away how well you perform the tasks learned in previous lessons.
Personally I'm a big flight sim enthusiast and my ratio of flight sim hours to real world flight hours is somewhere in the ballpark of 500 to 1. But even 1:1 will already have a huge effect because you essentially double the time.

Honestly, as a private pilot I couldn't disagree more with this. I think sim flying (especially home sim) is next to useless for the stick and rudder skills of private piloting. They can be very good for procedures, especially IFR and can be useful for practicing nav but I think chair flying is the best method of learning through your PPL. Additionally, there's a high risk of picking up bad habits while learning to fly without your instructor shouting at you

@Dan - Unfortunately, it is an apples and oranges comparison. A person can learn from a flight sim. If they take it seriously. The ratio of benefit from learning from home sims vs real flying is not 1:1. A ratio of 10:1 or even 20:1 would be generous. The biggest benefit is access & convenience. Having done FFS training at the AA training center, I can tell you it is darn near the real thing. FFS training is near 2:1. But, it costs more than time in a GA training aircraft. As you said, home sims can be good procedural trainers. But, there is no substitute for real flight hours.

@Jan - I agree with Dan. Flight simming is a very useful tool in training. It has its limitations of usefulness. As you have pointed out, you can develop and reinforce habits and routines. As Dan has pointed out, some of the habits you develop are not good ones. So, practicing something the wrong way first makes it harder to learn the right way. Learn it the right way the first time as well as the reasons behind it and why it’s important for you before you practice it. To do this, learn with an instructor first. Then practice it once the instructor is comfortable with your understanding of it

Yes a home flight sim cannot replace real world flights and actual flight lessons. It's just a tool that helps you practicing but you have to be careful not to enforce bad habits. That's why I suggested to get in contact with a flight instructor. I wouldn't say that it necessarily becomes harder to learn the right way but you certainly need the right mind set and have to know that what ever you have been doing in the flight sim may not be representative of the real world. With several different flight sims installed you're not as much at risk of learning the "wrong way to fly" though.

It may be comparable to riding a bicycle through town and then jumping straight into a car. Yes there are similarities and yes you may profit from having seen the street sings and what not but there are many aspects that a flight sim cannot capture. But still you will be able to learn faster than if you had no experience at all. Or at least this is what I have experienced with each person who used flight sims first and then transitioned to the real aircraft.

How much simulator training does an aspiring general-aviation pilot
  need?

None.  I've never had any simulator training, and I've made it through the ranks of "aspiring" GA pilot to reach the exalted status of "actual" GA pilot, and I've never crashed yet.  At least not significantly.0
Footnotes
0 = Not Significantly

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why have different flights with the same flight number?
It's not uncommon for two distinct flights to have the same number.  For example, DL10 consists of a narrow-bodied jet flying from Denver to Minneapolis–St Paul and then, two to three hours later, a wide-bodied jet flying from MSP to London Heathrow1; AA55 splits Manchester–Chicago–Orlando. This question gives another example and asks how ATC would deal with the situation where one of these flights is delayed leading to both being in the air at once.
But that begs the question of why one would give the same number to two flights in the first place. I understand that, historically, it was common for a long-haul flight to make several stops for refuelling but it's a long time since that was common and, here, we're talking about completely different aircraft and not just a refuelling stop.
What advantage is there to an airline in assigning the same number to two flights like this?

1 At least, it did when I posted the question in early October 2017. Now, a month later, it's a narrow-body from Kansas City to Minneapolis and then a Minneapolis–Heathrow flight. On some days, there's about 45 minutes between the two; on others, a little over three hours.

I suggest put the word advantage in the question otherwise others may think it's a duplicate without reading the whole question

@vasin1987 A duplicate of what? The question I linked to asks how to cope with this practice; I'm asking why it's done at all, which seems to be quite clearly different. (Of course, if this question is a duplicate of some other, that's fine.)

Strikes me as an excellent question, especially since airlines seem to tend to use 1- and 2-digit flight numbers for international (or at least trans-oceanic) flights, using a 2-digit flight number for a US-domestic leg. However, if one wanted to get from Denver to Heathrow, DL10 would be the way to do it, albeit with an annoying layover at MSP.

Related if not duplicate: Can two different planes share the same flight number? and Is a flight number unique for the schedule, origin and destination?

@FreeMan Quite a lot of flights between Los Angeles and the east coast have two-digit flight numbers. There are plenty of non-stop flights from LHR to DEN but DL10 with its layover is the only options with Delta.

@DavidRicherby - a quick Expedia search does not show DL10 as a DEN-LHR option. There are stops in ATL (not shocking), one in DET, and several in JFK, but no MSP, so that shoots my theory.

Re: LAX - east coast using 1-digit flight numbers. I did say tend... :)

@FreeMan If you search for DEN-LHR on delta.com, one of the options is the analogous DL16 (DEN-DTW-LHR with a change of plane) but, yeah, I can't get it to offer me DL10, or DL11 in the opposite direction (LHR-MSP-DEN). It's kind of interesting that even the airline doesn't seem to be pushing DL10/11 as if it were a single flight.

@FreeMan Perhaps we were having trouble finding tickets for DL10 because it now runs KCI-MSP-LHR. I would probably have been looking for tickets at least a month in advance to distinguish between "We don't sell this" and "You can't have a ticket because the plane is full."

As far as I know, this practice is mostly just limited to very large airlines in the U.S. The reason for this is that the airlines are so large that they'd literally run out of flight numbers in some of the allocated ranges. Usually the 9000 range is reserved for special flights (e.g. repositioning flights, or, as discussed in the answer to the linked question, when a different callsign is needed,) but other ranges are also reserved for things like codeshares onto the flights of partner airlines and for flights operated by regional carriers instead of by mainline.
For example, this post from this flyertalk thread lists the following ranges used by Delta observed by a frequent flier on that airline:

GoJet: 6000s
   Endeavor: 3000s
   Shuttle America: upper 2000s to lower 3000s.
   Compass: 5000s
   SkyWest: 4000s, 7000s
   Mainline: 0001-2999

From personal experience, I've noticed that partner airline codeshares on Delta are usually up in the 8000 range (maybe also part of the 7000 range?) Delta has a lot of partner airline codeshares, so quite a lot of the flight numbers go to this. Delta mainline operates a lot of flights. According to Wikipedia, Delta mainline and its regional carriers operated 5,400 flights per day as of October 2016. Having only 3,000 flight numbers available to mainline means that they'd almost certainly not have enough if they didn't reuse some of the numbers.
In total, according to Delta, their route network, include partner airline flights, totals over 15,000 flights per day. There are only 10,000 possible flight numbers and, when the reserved 9000 range is removed from consideration, only 9,000 possible flight numbers (or 8,999 if "Delta Flight 0" isn't allocated, which I expect it isn't.) As more and more of Delta's partner flights are given codeshares to Delta flight numbers, it would be very easy to exhaust the entire range of possible flight numbers.
An additional reason (possibly more relevant historically than today) is that it allows the airline to have a "direct" service to a city it doesn't actually fly to non-stop. Nowadays, people commonly use the term "direct flight" to mean "non-stop flight," but that's not the technical use of the term in airline-speak. The term "direct flight" really just means "we have a flight that gets you from A to B, but it might stop in C and D along the way."
Back in the day, this made more sense, as it wasn't as common for aircraft to have enough range to connect cities non-stop. So, a flight from New York to Seoul, for example, would typically stop in Anchorage to refuel before crossing the Pacific. Going even farther back, the first trans-Pacific flight (from San Francisco to Manila) had stops in Honolulu, Midway, Wake Island, and Guam. Since almost all of the passengers were going from San Francisco to Manila (not to, say, Wake Island or Midway, which were previously uninhabited,) it made sense to have a single flight number rather than using a different one for each segment. Nowadays, however, due to the much longer range of aircraft, there's not as much need for 'direct' flights with stops.

Pan-Am's SFO-MNL route via HNL, Midway, Wake, and Guam

There's also the pattern where back-to-back flights AAA-BBB and BBB-AAA, on the same plane, share a number.  I associate this with going out and back from a hub.   In the cases I'm familiar with, American (hub at PHL) runs PHL-ATL-PHL flights and Delta (hub at ATL) runs ATL-PHL-ATL flights.

@MichaelLugo: That's arguably "just" the same flight - a single directed path forming a cycle (in graph-theory terms).

I think the reason for situations as described is the limited number of "good" flight numbers, compared with the number of flights -- especially when codeshared flights are considered.
Generally, airline flight numbers are from one to four digits.  There are cases where a letter gets appended, although this seems mostly reserved for special cases, and is not a universal practice.  So in theory, that would be 9999 possible flight numbers, which seems like it should be enough to more than cover any airline's schedule (a few thousand flights max) in a day.  However...
Some ranges of flight numbers get reserved for things like charter flights, maintenance ferries and other aircraft repositioning, and "stubbed out" flights.  The latter occur when, for instance, flight 123 is scheduled to operate from AAA to BBB to CCC, but the AAA-BBB flight is running so late that the airline decides to use another aircraft & crew (if they weren't already) and operate the BBB-CCC leg on time.  That latter leg needs a new flight number, since you can't have two "flight 123" in the air at once.  So some range of flight numbers gets reserved for use in situations like that, and ATC sees flight 9123 (or 9001) operating the BBB-CCC leg that day.
Beyond this, codeshare flights get a flight number.  Often, when airline X sells a ticket to their customer so that he'll fly on a flight operated by airline Y, the flight will have both an airline Y flight number (which is what ATC will use) and also an airline X flight number (which may be printed on the ticket & may show on the monitors in the airport).  So while the passenger's itinerary may say Airline X flight 12 AAA-BBB and Airline X flight 7422 BBB-CCC, the reality may be that the second flight is really Airline Y flight 1422.  But to make things look like you're flying entirely on Airline X, that carrier uses the 7xxx range of flight numbers for their codeshare flight. Considering how large the codeshare networks can be, that could easily run to several thousand flight numbers reserved for this purpose. (As reirab's excellent answer clearly demonstrates.)
So they start to run out of numbers, and the desirable numbers (i.e. low & recognizable, like 10 or 12 or 200) end up being reused.  Thus the frequent flyer knows that he always catches flight 76 at 9:00 Monday morning from AAA to BBB, which is easier than flight 5976 today and flight 3921 last week and some other long identifier next week.  He doesn't care that after BBB that same flight number is used an hour later, perhaps with another aircraft and crew, to go on to CCC. He's just taking the same "flight 12" that he's taken for the last several weeks or months.

If you allow leading zeros eg BAW007 is considered valid and of course different than BAW7, then you have more than 9999. 11110 if I calculated correctly :D

@SteliosAdamantidis  I've never seen or heard of that convention.  Flight numbers are almost always used at ATC callsigns, and those may PAD a single-digit flight number with leading zeroes in many cases, but they certainly don't differentiate flight 7 from flight 07 from flight James Bond from flight 0007.  So I don't think anybody is actually able to expand the range of usable callsigns that way.  Would work fine in computer code, but not so well for human factors.

Sorry I don't understand you, you say it can't happen or it doesn't differentiate them? There was the ill-fated KAL007 (that some believe it was in a James Bond mission) so it can happen. As if it doesn't differentiate, it does, though it's a good practice not doing it for avoiding call-sign confusion

@SteliosAdamantidis  Flights may be referred to as KAL 7 or KAL 007, but it's two ways of referring to the same flight.  Nobody uses leading zeroes to differentiate two separate flights, at least as far as I've ever seen. Not saying that a different ATC system couldn't use the convention where flight 1 is different from flight 01 and flight 001 and etc, but AFAIK from a couple decades of observation, that isn't the way it's done in US (or worldwide) ATC today.

If you're splitting an AAA-BBB-CCC flight (let's call it flight 1234) into AAA-BBB and BBB-CCC parts because the AAA-BBB part is running really late, that seems like a good use case for appending letters to distinguish the off-nominal situation (for instance, designating the BBB-CCC part as flight 1234A).

flight number is colliquial for the IATA flight code used in booking systems.
As FreeMan has observed correctly, shorter flight numbers identify longer or otherwise more premium (i.e. business class only) flights.
The same number only refers to the route and may not only change the aircraft, but also the airline operating the flight (leg).
The examples you have provided are each one flight with different legs.

Thanks for posting but I don't see how this answers the question at all. In what sense is it "one flight" when you go from Denver to Detroit in one plane, getting off that plane, sitting in Detroit for a couple of hours and then getting on a different plane to fly to London? Why is DEN-DTW-LHR sometimes considered as a single route but most often (even by the same airline) considered as two separate routes. Specifically, as the question says, "What advantage is there to an airline in assigning the same number to two flights like this?"


text:
How do the Airbus Beluga's wing/control surfaces deal with its high center of gravity?
This is the Beluga:

It's used for carrying pieces of a fuselage (of much larger planes) from one place to another so they can be fitted together to make a plane.
As I recall, it's based on an Airbus A300, and then they added on the huge bulging fuselage piece so it could carry more stuff and moved the cockpit down a bit to make way for the huge door at the front of the bulge.
My question is what did they do in terms of wing/control surface design to keep the plane from becoming unstable.  Clearly when this plane is fully loaded the CG is much much higher than a regular A300.  Which seems like it would make it more likely to want to tip over in some fashion. What did they do to counter-act this?

added roll stability in the envelope protection.

@ratchetfreak lol, right, but how?

the payload is only a third of the MTOW (47t/155t) It's mostly for large but light cargo.

@ratchetfreak 1/3 of the total weight seems like...a lot of weight.  I'd still like to know how it's accounted for.

if the empty CoM aligns with the floor of the cargo hold then in worst case (uniform cargo filling up the entire hold) the CoM would move up 2.3 m. I'd have to boot up my KSP to find out how that affect handling.

@ratchetfreak: Did A300-600ST get envelope protection retrofitted? Because A300 did not have them (they were introduced in A320).

As long as the aircraft flies without much sideslip, the vertical position of the center of gravity is not important.
It is a common misconception that the aircraft could "tip over" when banking due to a high location of the center of gravity, or even that dihedral would right the aircraft up because the lower wing will create more lift. This is all wrong!
To understand why, look where gravity is pointing in banking flight. By gravity I mean the total acceleration felt by the pilots and passengers, the apparent vertical direction.

A320 front view straight and banked with force vectors in the aircraft's frame of reference.
The force vectors in banked flight don't differ from those in level flight, only their magnitude grows. In both cases the apparent vertical is parallel to the vertical plane of symmetry and will go straight through the center of gravity, regardless of its vertical location. Therefore, it has no lever arm and produces no momentum around the center of gravity.
To put it another way, the aircraft banks in a coordinated turn to keep the apparent vertical in its vertical plane of symmetry, now that a horizontal force needs to be added to change the aircraft's angular momentum.
Therefore, neither the wing nor the control surfaces need any special adaptation to the huge fuselage. Only the vertical tail needs to be increased to compensate for the increased side area ahead of the center of gravity. In case of the Beluga, two vertical fins were added and the strake enlarged. This is a very common procedure for modifications of existing aircraft, because it is easier than designing a new vertical and improves handling compared to a new, scaled-up fin.

Side view of the Airbus Beluga (Picture source)
The fuselage has its aerodynamic center ahead of the center of gravity, so increasing its size will also increase its destabilizing yawing moment in a sideslip. This requires more stabilizing area at the rear, which can be kept relatively small since its aspect ratio is much higher than that of the fuselage, making it more responsive to sideslip angle changes. Both together will create a side force in sideslip which will be substantially bigger than that of an unmodified A300 in the same conditions. This sideslip-induced side force and the drag which comes with it will make the flying characteristics of the Beluga different to that of an A300. Since it acts quite a bit above the center of gravity, it will add a rolling moment, increasing the dihedral effect. I expect that it will be harder to build up a sideslip angle in the Beluga, and if the pilot crosses controls, the aircraft will slow down more quickly than a regular A300.
When designing the Beluga, it was clear from earlier planes (Super Guppy, 3M-T or BM-T Atlant) that the oversized cargo bay would not make flying impossible.

The 3M-T/BM-T modification for rocket stage airlifting. Picture source.

Peter nice answer but there is one thing that totally confuses me: The vector of centripetal(?) force drawn to the outer opposite of the turn. Shouldn't it point to the direction of turn like it's shown here?

@SteliosAdamantidis: The shown vector is that of centrifugal force, which is the apparent force in accelerating (rotating) reference frame that behaves similarly to gravity.

It would be nice to add what happens if there is a side-slip as it explains why it needs the additional vertical stabilizers (the question says control surfaces, not specifically ailerons)

@JanHudec Centrifugal force is not a real force and thus not suitable for circular motion calculations. Even if it is, ΣF is 0 according to the picture and with no forces applied you cannot change your motion state (ie accelerate or decelerate) and thus you cannot turn.

@SteliosAdamantidis: In the rotating frame of reference (the one relative to the aircraft) the inertial (centrifugal) force exists and must be included in calculation and the result is that the forces are in balance and the aircraft is not accelerating, which relative to itself it isn't. In the inertial frame of reference there is no centrifugal force and the centripetal force (which is the horizontal component of the lift force) causes the plane to turn. The picture shows the forces as appropriate for the airplane-relative, rotating, frame of reference.

I agree that if the aircraft is turning while banked the forces will not be very different, but the force needed from the ailerons to roll the aircraft will be affected.

@foot: There are many minor differences, like the axis of roll which is above the cockpit. This creates a sensation of shifting sideways when the ailerons are deflected and the aircraft rolls. But the same is true for the 747, where the pilots sit above the axis of rotation. It does not make flying the Beluga fundamentally different.

As we can see in the above picture, an aircraft's center of gravity (CG) always lies at the intersection point of the three axes. So whenever CG is shifted along one axis, it affects the other two also.
When CG is shifted vertically (along vertical axis), it affects directional stability. In such case, rudder is needed to ensure directional stability.

The unusual bulge in the fuselage of an Airbus Beluga may make one think it can carry more weight than the A330, but that is not correct. MTOW of A330 is between 364,000-378,500 lbs, however Beluga's MTOW is 341,713 lbs.
Since CG does get shifted upwards in Beluga, it affects the aircraft's directional stability. It has been mentioned at several places (Wikipedia and here and here) that the tail of Airbus Beluga has been enlarged and strengthened to maintain directional stability.

Image Source

I don't think the CG is affecting the directional stability, it's more the increased surface area forward of the CG, and reducing the effectiveness of the stabilizer behind the enlarged compartment.

The tail surface has clearly been upsized, see this shot of several Airbus's http://www.allaboutguppys.com/beluga/ai-fama.jpg with A320, A321, A310, A300-600, A330-200, A340-300, and the A300-600ST "Beluga".  More info here including "The fin was also changed to maintain stability in flight. " http://www.allaboutguppys.com/beluga/600stf.htm

@CrossRoads: According to Wikipedia, the Beluga's vertical tail is a stretched A340 model rather than that used on the stock A300.

authors: Георгий Борисов


text:
What is the function of the Apache's Strap Pack?
I have recently been reading about the issues with the Apache's (AH-64) strap packs. I've read that the strap pack holds the rotor blades on to the hub.
However, it appears the blade also connects to the pitch housing assembly. So I don't really understand the function of the strap pack and why it's failure would cause a catastrophic failure leading to loss of aircraft.
Questions:

What is the Function of the Strap Pack?
Why does its failure lead to loss of aircraft?
Is this a common design on other helicopters?

Reference: Story

Image Source

Picture above is from Helicopter Performance, Stability, and Control by Ray Prouty, and shows the fully articulated rotor such as installed in the Apache. The Fully Articulated term means that the blades can rotate in three Degrees of Freedom: fwd/aft, up/down, and nose up/down. The rotation axes are single points of failure: when they break the blade is launched, unbalancing the rotor and rendering flying and autorotation impossible.
The problem with the Apache setup is with eight nuts degrading due to corrosion, as from this link:

The order came after officials learned that bad weather and salt water in coastal regions could lead the eight “strap pack nuts” on each of the rotary blades to reach the end of their life expectancy sooner than projected.

Fully articulated hubs are the most common design in helicopters, the others being the teetering rotor such as in the Bell 212 and the hingeless rotor in for instance the Westland Lynx.

So the "Strap Pack" is the 8 nuts that attach each blade to the 3DoF hing? I'm getting more understanding from your answer than I had from the question, but it's still leaving me at a loss. It doesn't feel like it really answers the question, but maybe I'm just not understanding the answer....

@FreeMan I don’t have a picture of the actual Apache hub, unfortunately, and had not heard of the term “Strap Pack” before. This article did seem to confirm though.

The strap pack is the Y looking object in the bottom left of the figures in the question. It is a series of metal straps laid on top of each other.

The strap pack is the structural member which transmits loads between the blades and the pitch housing assembly. Not shown in the drawing above is the shear pin that goes down through the hole in the pitch housing and through the holes in the strap pack members. The pitch housing ends at that junction and there is no other connection between the blades and the pitch housing.

Could you re-word this a little bit or add a figure? I think I understand what you are saying, but not 100%. Is the strap pack what is transferring the radial load from the blade back to the hub and the pitch housing can't actually handle the radial load?

the strap pack is the go-between that transfers radial loads from the blades to the pitch housing through the shear pin.It's a way to mate the blades to the pitch housing; the pin joint is there to allow the blades to flap fore and aft.


text:
How can compartment bay loading informating be derived from the IATA load message (LDM)?
In the IATA Airport Handling Manual procedures, messages are send to communicate with the transit station to describe the cargo load. The Load message LDM (AHM 583) is sent primarily to enable the transit station to know in advance the load which continues on the same aircraft.

LDM ZZ999/13.ZZOEA.Y136.2/4
  -SHJ.15/22/3/1.T1500.3/1000.4/500.PAX/40.PAD/0
  -CMB.27/22/12/3.T3500.1/2800.5/700.PAX/61.PAD/0 SI

In here we got  hold id 3 total gross weight 1000kg,...
In our automated system, we need info in compartment bay level.
How can we get those information?

Any other message like Container / Pallet Distribution Message CPM (AHM 587)?
Or we have to manage manually (should distribute by load controller)

It's related to IATA Telex, but the question is definitely unclear.

thanks @mins yep It is related with IATA telex.. I parsed those LDM message. but those details are in abstract level (e.g total gross weight 1000kg in hold id 3 --> refer 3/1000). how can we get some specific details like what is the weight distribute in compartment bay (32L). note several compartment make a hold level. can any one who handling AHM messaging / Sita telex plz help me

I'll edit your post to make it more readable for this community. If you want to roll back to your version and improve it on your own, just use the edit link. You should still explain the context: Are you a developer or a user? Are you using an application or an API? Which one?

Paranee,
There is no such detail in the LDM, it is just a WEIGHT value. There maybe specifics for certain SL/DG (review AHM again for those) as some SL/DG are required to show location and some location and weight - explained in AHM.
BUT - LDM is just an overview, not very specific as it does not need to be. For a through flight A>B>C, where A is OFFLINE to your system, if you have received teletype LDM for processing and you are doing the sector B>C then any load B>C is just shown (know by the system) as TRA (transit) load - nothing more. No more detail.
However for unitized aircraft, the CPM complements the LDM to show the detail required by bay as opposed to HOLD and/or COMPARTMENT.


text:
What is the purpose of the arrow on the flightdeck of USS Franklin Delano Roosevelt?
The below photo of Midway class aircraft carrier USS Franklin Delano Roosevelt shows a long white arrow starting on the centerline of the flight deck and continuing up until the "42" at the bow.
I initially thought it might be a guideline for when AV-8A Harriers were deployed to the carrier as these weren't capable of taking off using the catapult, but that didn't happen until 1976. The photo is from 1969 according to Wikipedia. The same arrow is also shown in a 1971 photo
What was the white arrow for?

"This Way Up" when it's packed for storage

I assumed it was to guide the seamen so they knew where the front of the boat is...

That’s a deck launch arrow.
As shown above with the Harriers and prior to the 1990s, certain aircraft were permitted to deck launch under their own power, under certain weight and loadout restrictions, without using a catapult assisted takeoff.  Deck launches were very common from the beginning of naval aviation through about the Korean War, but began to fall out of favor with the advent of jet aircraft and their higher stall and takeoff speeds.  They also interfered with the flow of traffic on the deck on the larger carriers equipped with an angled landing area.
The deck launch arrow typically starts midship at the LA centerline (near the  Jet Blast Deflector for the #3 waist catapult on the larger ships) and runs all the way to the bow of the ship. Depending on loadout a pilot would simply begin their takeoff roll there, under their own power and off the bow of the ship, similar to the launch procedures on the Russian Kuznetsov-class STOBAR carriers. The US Navy finally eliminated the procedure aboard its CATOBAR carriers 30 or so years ago.

I don’t see a waist cat.  I don’t believe the converted straight decks had them.

So its a "this way to sky" because conditions (dark/smoke) make obscure where the edge of the deck is, and pilots might take off sideways in error.

@Michael Hall You can see them on converted Essex- and Midway-class carriers.  And they were definitely present on older Forrestal-, Kitty Hawk-, and even early Nimitz-class ships had them.  They disappeared from flight deck marking by the 1990s

I meant that converted straight decks didn't have waist cats, not that they didn't have these deck launch centerline marks.  While it doesn't directly say so, your answer hints that there might be a #3 waist cat on the photo in the question.  I'm not confused, but somebody might be...

@Michael Hall the Essex-class ships did not, but Coral Sea (CV-43) did have a single waist cat.  Midway (CV-41) did have a single waist cat after her first refitting in the early 1950s.  This was eliminated during her second refitting during the 1960s as she had become dangerously unbalanced with the new refit, particularly in rough seas.

It is the marking showing takeoff direction for non-catapult, STOL type aircraft. Here you see a pair of Harriers directly aligned, with yellow shirt "shooters" in control.

The original picture from 1969 was pre-Harrier.

@WPNSGuy Harriers are one example of STOL aircraft.

Yes they are STOL. But that marking existed before Harriers, so it was for something else. Helicopters, possibly. Denoting the normal wind direction on the deck, as the ship is underway.

@WPNSGuy You missed the point. The line was for non-catapult aircraft. Harriers were not the first.

@WPNSGuy, to give an example of pre-Harrier STOL, in 1963, the C-130 Hercules demonstrated the ability to land and take off from an aircraft carrier.  Pictures of the tests show markings very similar to that arrow.

Prop driven aircraft of the 1950s and 60s would often deck launch once the catapults had cleared enough forward space.

It is known as the free deck launch line. Someone already correctly stated that it was for certain aircraft (C1 Trader, S2 Tracker) to launch without use of a catapult. All painted lines on aircraft carrier decks are known as VLA (visual landing aids). It doesn't matter if the lines have anything to do with landing, they are still covered in the VLA manual. Prior to 1984, the free deck launch line was painted on every aircraft carrier. By the way, USS Coral Sea did have a waist catapult.

Your answer would be improved if  you could add a reference showing this.

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.


text:
What is the difference between SMOH and SFOH?
When looking at aircraft for purchase online, a lot of acronyms are used.  In particular, the SMOH and SFOH acronyms are thrown around a lot for used aircraft.  What are the differences between these acronyms, and what are their purpose for a potential airplane buyer?

"Since Major OverHaul" vs. "Since Factory OverHaul" according to google

With many airplanes the longevity of the engine is a major factor in the price of the aircraft. Piston aircraft engines are generally good for 2000 hours of operation before they need to be overhauled, which is almost always painfully expensive. The more life left on the engine the higher the value of the airplane. SMOH and SFOH both have to do with the time since the engine was overhauled, both are in hours:

SFOH = Since Factory Overhaul
SMOH = Since Major Overhaul

A factory overhaul means that the engine was sent back to the manufacturer for its overhaul, where a major overhaul could be done by anyone. In general factory overhauls are consistently good whereas non-factory overhauls vary more in quality. Factory overhauls are more expensive as a result.
If you see an airplane that has 300 hours since overhaul then there's plenty of life left, if you see one that has 1700 hours on the clock you know you are going to have to fork out a lot of cash much sooner, but you can get the airplane much cheaper.
Another acronym you may see is SPOH, that is Since Prop Overhaul. Variable pitch propellers also have mandatory servicing requirements, and although less expensive it's still not cheap, so a factor in the cost of the airplane.

This is not necessarily true.  Freshly overhauled engines are more likely to experience failure than a well used engine, up to a point.  Also, SFOH does not necessarily mean better quality.  A certain manufacturer is known to have terrible cylinder quality assurance and consumers sometimes send cylinders off for rework very early on in the engine's live to get ahead of undue wear.  It is not uncommon to see well run engines achieve 2500hrs without anything more than some top end work.  Typical C/S props do not have mandatory inspections aside from ADs (in the US).

The life of an aircraft engine is measured in hours of operation since some major service was done to it. When looking at ads for planes there are three regulatory terms that you'll see in engine descriptions:

New (TSN)
This one is pretty self explanatory - A brand new engine, produced with all brand new parts that comes to you right from the factory (or an authorized dealer).

New engines have a "zero-time" logbook and no operating history because they've never been installed on an aircraft. Usually there's a "test cell run" entry in the logbook, if anything.

Rebuilt (There's not a common abbreviation here - I've seen SFRB or SFRM)
An engine that went back to the factory and was rebuilt to the same production limits as a new engine. Some of the parts in the engine will be new, some may be used, but all will meet the same standards and specifications  as a new engine.

Only the original manufacturer can rebuild an engine, and it comes to you with a zero time logbook and no operating history (because a rebuilt engine is done by the factory and is to new-engine limits and may be made up of components from a bunch of other engines there's no way to give it a history, so it's treated the same way new engines are).

Overhauled (SMOH or SFOH)
An engine that has been completely disassembled (the crank case is split and all the parts pulled out), extensively inspected, and reassembled to either service limits or new limits. An overhaul usually includes some used parts (frequently from the same engine), and new parts as necessary to meet limits.
An overhaul can be done by the factory ("SFOH" - Since Factory Overhaul), or by a specialty engine shop, or even by your local A&P mechanic (both "SMOH" - Since Major Overhaul).

Overhauled engines retain their operating history, and should have a complete set of logbooks since the day the engine was manufactured. Even if the only part that gets reused is the engine case an overhaul is still "the same engine" in the FAA's eyes, so make sure you can trace the full operating history of that engine.

You will sometimes see another term - "since top overhaul" (STOP or STOH), but this one is not actually defined in the regulations. Generally it means a shop removed and replaced all the cylinders (the "top end"), but did not open the crank case and thus may not have inspected the "bottom end" (crankshaft, camshaft, bearings, etc.)

The terms "overhaul" and "rebuild" are defined in 14 CFR 43.2, and further expounded upon in AC 20-62E:

§43.2   Records of overhaul and rebuilding. (a) No person may describe
  in any required maintenance entry or form an aircraft, airframe,
  aircraft engine, propeller, appliance, or component part as being
  overhauled unless—
(1) Using methods, techniques, and practices acceptable to the
  Administrator, it has been disassembled, cleaned, inspected, repaired
  as necessary, and reassembled; and
(2) It has been tested in accordance with approved standards and
  technical data, or in accordance with current standards and technical
  data acceptable to the Administrator, which have been developed and
  documented by the holder of the type certificate, supplemental type
  certificate, or a material, part, process, or appliance approval under
  part 21 of this chapter.
(b) No person may describe in any required maintenance entry or form
  an aircraft, airframe, aircraft engine, propeller, appliance, or
  component part as being rebuilt unless it has been disassembled,
  cleaned, inspected, repaired as necessary, reassembled, and tested to
  the same tolerances and limits as a new item, using either new parts
  or used parts that either conform to new part tolerances and limits or
  to approved oversized or undersized dimensions.

There is no difference between a "factory" overhaul and someone else's "major" overhaul - at least according to the regulations: The standards for what constitutes an overhaul are the same.  What is different is who you talk to if the engine breaks (for a factory overhaul you would go back to the factory, for an overhaul by an engine shop you would go to the shop, and for one by your local mechanic you would go talk to the mechanic).
If you're looking at a plane which has had an engine overhaul (the vast majority of the used piston GA fleet) you should pay attention to where it was done and the reputation of the overhauler, but given two engines, one overhauled at the Lycoming factory and the other at a reputable shop like Penn Yan Aero, they would generally be considered equivalent.

There, have another Nice Answer badge.


text:
Does an aircraft's nose landing gear extend on take off?
Something I noticed while flying - while on takeoff it feels as if the plane is tilting upwards even though the plane is clearly still on the ground with all sets of landing gear.
Does the nose gear extend immediately upon acceleration to perhaps generate more lift? Or maybe it's just an illusion caused by the acceleration. (I've only noticed this on large aircraft - like for example: Airbus A320 or Boeing 737.)

No, the gear doesn't actively extend, and any passive change to the strut extension during takeoff is likely to be imperceptible.
What you are perceiving during takeoff is the somatogravic illusion. It is a physiological sensation, not a physical change. Rapid acceleration, as during a takeoff roll, causes the inner ear to report what your brain assumes is your head tilting back.
The otolith organs in your inner ears sit in fluid and detect the tilt of your head. Acceleration and pitching up (or tilting back) cause the exact same movement of the otoliths. Because the otoliths are pushed backwards by the fluid, just like they would by you tilting your head back, it feels like a climb.
When an airliner is taking off, you have limited outside references to the horizon and your inner ear takes over the task of orienting you. You might notice it in smaller aircraft if you closed your eyes; in very small aircraft, the acceleration may be too slow to trigger the illusion.

It can be readily observed in other vehicles too. Easiest in the tube, where you don't have outside reference (the small windows in airliner play a role here). If you stand, look at a vertical handlebar (and not out) and try to stand straight you'll notice it. And of course the same effect in opposite direction when decelerating, which is more pronounced since most vehicles brake better than accelerate.

+1 Nice answer. Note that this same effect is (ab)used in the opposite direction in flight simulators: tilting the cabin back (pitch up) creates a false sense of acceleration for the occupants.

@JanHudec - During takeoff, there is a very real physical change - is there some sensation above that? The change is that the acceleration of the plane and the gravity add up to the acceleration you experience, in a physical way. The gravitation is acceleration in direction of earth of about 9.81 meter per second per second (m/s2). It  sums up with the planes acceleration. Your weight increases (not your mass!), but your down direction changes too, and it is not physiological, it is perfectly real physics. The normal gravity is no longer there for you, physically.

@VolkerSiegel, of course it is perfectly real physics and there is no sensation “above” that. The point is that because you can sense the direction of weight quite accurately, but rotation and magnitude of weight very coarsely if at all, the feeling is indistinguishable from, and therefore automatically interpreted, as tilting, though something else is actually going on.

I'm assuming you are referring to the 'tilting backwards' that occurs when the aircraft begins its takeoff run. There is of course a much more pronounced tilting backwards when the nosewheel actually lifts off the runway, a few seconds before the main wheels come off.
This tilting at the start of the takeoff run is actually a sensory illusion. It's caused by the acceleration of the aircraft. The forward force on you from the seat is combining with the upward force (resisting gravity) makes it seem as though the aircraft is tilting, when in fact it isn't. You would get a similar effect in a fast-accelerating sports car; however in a car you have a clear view of the outside world which means your mind can understand that this is acceleration, not a tilt.
You can check this in a number of ways: 1) if you watch a plane taking off from outside, there is no noticeable tilt of the plane, nor any noticeable change in the nosewheel extension - certainly nothing like as much as the tilt appears to be from the inside 2) Looking at the outside world through the window will confirm that the plane is not tilting 3) This effect occurs on planes with engines both above and below the wings, which you would not expect if it were an actual tilt.

I will assume you refer to the initial acceleration when you speak of "while on takeoff", since after the rotation the answer would be quite tautological.
Let's be clear, the nose gear does not "extend" anywhere during take-off since its damper/shock absorber is not an active component, but rather a passive one.
The effect you are feeling is due to the acceleration and the inertia of the aircraft: the engines of a large aircraft sit below the Center of Mass which will incur a rotational force to the aircraft, lifting the nose up a bit. The weight will be "sitting" more on the main gear rather than the nose, you have a similar effect on a car or, more notably, on an accelerating motorcycle.
You also have the reverse effect when decelerating: the weight will tend to stress more the nose gear rather than the main gear, the same way a motorcycle tends to "sit" on the front wheel when stopping.
On aircraft with the engines up high the rotational force will be reversed until the elevators have enough airflow to counteract it.

it's important to note that that only happens with airplane with engines below the center of gravity, if they are above the nose gear will get pushed down as well until there is enough airflow for the elevators to over come that.

@ratchetfreak you are totally correct! would you like to edit my answer?

Interesting. I'll be sure to share this knowledge next time i fly.

Are you sure this is right? I think it's more likely to be an acceleration illusion.

@DJClayworth from the physics point of view, it is absolutely right.

I understand that there is some shift of weight off the nosewheel onto the mainwheels, but does the nosewheel actually extend enough to account for the perceived tilt? Can you show me videos of taking off planes where the plane actually tilts at the start of the takeoff run, or where the nosewheel extends a significant amount? (There are some videos of that not happening in my answer).

@DJClayworth saying that it happens and saying that it is noticeable are two different things.

This is almost certainly not the cause of the sensation @codedude describes - it's physiological, not physical, and it's well documented by the FAA, NTSB, and NASA research!

Also, the center of mass is well ahead of the wheels. Would the thrust not push the nose down regardless of engine location?

Are the landing gear struts really able to be compressed enough that you'd notice the change in physical angle?

@egid, I seriously doubt such a configuration would ever be used, given the sollecitation it would cause on the nose strut during landing

@DavidRicherby see my last comment to DJClayworth

@Federico, the cg in most airliners is going to be at least 5-10 feet in front of the gear. I'm not quite sure where you are suggesting the CG is relative to the gear otherwise.

@egid 5-10 feet on a CS-25 aircraft is negligible, is not "well ahead"

-1 because while this negligible effect may occur, it is not responsible for the sensation the question is asking about.


text:
Is an "atmospheric geostationary satellite" feasible with current technology?
Meaning by "atmospheric geostationary satellite" a vehicle capable of hovering 30 km above Earth surface, hence insde atmosphere, for unlimited time, making use of air propellers, solar panels and batteries.
How much energy is needed to keep an object steady in air at 30 km above surface?
There are two possibilities: a plane-like vehicle, flying in circle, using wings to stay up; an helicopter-like vehicle, hovering.

3 possibilities: add balloon.  30 km is 98,425 feet.  That's (I think) the high end of weather balloon country.

Scientific balloons with heavy payloads get up to 120,000 ft.  Though balloons are never stationary, unless tethered.

Why 30 km?  Why not circle lower?

@MarkAdler Blimp?  Solar powered electric motors for station keeping?

I mention that in my answer.  However fighting the winds up there with all that cross-section would require tremendous power.

@MarkAdler To avoid interference with commercal flights.

I don't think any commercial flight gets above 15 km.  (At least now that the Concorde isn't flying anymore.)

Google have just bought a company working on developing this sort of thing.

closely related

Short answer: No.
Long answer: Your "unlimited time" condition makes the short answer easy. If you need to go up for a limited time, and you have the liberty to choose the time of ascent and descent, the answer is: Possibly.
First, there are two ways of going up there: A balloon and an aircraft. A helicopter would be much less efficient, the tether of a balloon will be too heavy to lift, and you will see that even a glider-like aircraft will struggle to stay for some time at 30 km.
Next, atmospheric pressure at 30 km is 12 mbar, just 1.2% of what it is on the ground. So your aircraft has to go at some speed just to create enough lift. If we assume that you fly at Mach 0.5 to 0.6 (where high-lift airfoils and propellers can still operate), your dynamic pressure is that of a modern glider at low speed. The flight speed actually is between 150 and 180 m/s, however.
Now let's assume your aircraft has an L/D of 50. This translates into a power requirement just to stay aloft of 3 to 3.6 kW per ton of aircraft mass. Your propeller will have no more than 85% efficiency, and your engine will create some loss as well, so your installed power needs to be at least 4 kW per ton of aircraft mass. Since you fly at a glider's dynamic pressure, you will also have a glider-like wing loading of 30 kg/m². Per ton, your wing area is 33.3 m². To operate an air breathing engine at this altitude is a challenge, so I will assume solar electric propulsion. Let's be optimistic and we assume a solar constant of 1.4 kW/m² at this altitude, and you fly at moderate latitudes (say, 45°), so your solar panels can create (20% efficiency) 200 W per m² or 5.3 kW per ton of aircraft mass (assuming 80% of the wing is covered, the rest will have too much curvature). Of course, this is all valid only around noon, so if you want to stay overnight, even in summer there is not enough energy to keep the aircraft up for a longer time, even with very optimistic assumptions. You might want to assume batteries which can provide the power for the climb phase, so you take off in the middle of the night and arrive (with empty batteries) at altitude in the late morning. Then you might really stay there until 2 or 3 pm, when the lowering sun means that your solar panels will not provide enough power to stay up, let alone charge the batteries. And I have not even started to subtract the power for operating any equipment (which would be the reason to go up there in the first place, right?).
To go with a lower wing loading means you will have a very delicate structure which cannot cope with the winds at 30 km and gust loading at lower altitude.
This wind will also be a problem for any ballon. 20% of winds at 30 km are above 76 m/s (Mil Std. 210C), 5% are even above 98 m/s. One cubic meter of helium gives you 10 N of lift at sea level, but only 0.156 N at 30 km. To lift one ton of balloon up to 30 km, you will need 63,000 m³ of volume. This is a sphere with a diameter of 50 m! The wind forces to keep this thing tethered will need a strong and heavy tether, so without going into the details I think that a tethered balloon will be a challenge, to put it mildly.
The "Facebook drone" articles are not serious, they are meant to create some P.R., and don't hold your breath for Internet delivered by drones anytime soon.

Even harder than the tether is a balloon envelope that could survive being held against a high wind.  However one million cubic meter 36 km altitude balloons are flown regularly, carrying 3600 kg payloads, so your 63,000 cbm doesn't really deserve an exclamation mark.  However those balloons are designed for low relative wind conditions, since they float with the wind.  They are made of essentially garbage bag thickness plastic, which would rip to shreds against a strong wind.

You've answered the question which asked about 30 km. However the Facebook drone article I saw said 20 km. By my BOTE the atmosphere's 16 times as dense than at 30 km.

The lower altitude translates into MUCH less coverage. My verdict on the "Facebook drone" stands.

Ok so 30 km is not feasible; 20 km is feasible but not practical due to low coverage. Which should be the lowest possible altitude not to interfer with commercial flights? 15 km? 10 km? I think the lower you go, the smallest vehicle you require.

I wonder if it would be possible to have some hundreds of steady vehicle flying as low as 500 METERS above, kind of a cellular network without poles, just to cover a single city without need to build anything, just launch.

maybe it's a problem of finding an "energy equation" and minimize it for mass and altitude? (it's actually not exactly a matter of "how much power" but "how much energy").

Not that much less coverage. At 30 km altitude, footprint radius is 970 km. At 20 km altitude, footprint radius is 792 km.(792/970)^2 is about 2/3.

@jumpjack: Anywhere above FL500 you are free to go; ATC is only for FL500 and below (except in restricted areas). The higher you go the more complex will be the propulsion system, so 15.3 km gives you indeed the simplest design for "Facebook drones". But if you compare the cost for connecting a metropolitan area with fiber and base stations against covering it with drones, cable wins easily over the long term.

@HopDavid: I wonder where you get your numbers. At 20 km the horizon is 500 km away, and if we assume line-of-sight connections, your footprint has a diameter of 1000 km. Area increases with the square of altitude if we disregard earth curvature effects which indeed limit area growth at higher altitudes. At 30 km, this effect is still small. So going from 20 to 30 should give you more than twice the coverage.

@PeterKämpf No, area doesn't square with altitude. I attached an illustration to my answer. Evidently I made an arithmetic error in my earlier calculations. But I still get the same result that a 20 km drone has an footprint 2/3 the area of a 30 km drone.

@PeterKämpf For some countries (including the U.S.,) Class A airspace goes up to FL600.

In 2003 NASA's Helios solar-powered aircraft made it up to 29.52 km (rounds up to 30 km!).  Alas, it broke up in flight, and I can find no reference of a follow on.  A plane would be more energy efficient than a helicopter, even a helicopter in forward motion, so I expect a plane is what you would see first.  The problem of storing energy and flying at night may be insurmountable.  (Perhaps beaming microwave energy to the aircraft?)
You could almost imagine a blimp or dirigible with propulsion to fight the wind, but it would be difficult to get much payload at that altitude, and the wind up there is fast.  So, no way.
If you don't mind a long line that aircraft would have to avoid, a kite is another possibility, and would solve the problem of power for the payload at night.  There are pretty constant winds up there, so if you can get it up, you can imagine a kite flying for a long time.
A tethered balloon could in principle work as well, and would have more payload than a free balloon trying to fly against the wind.  However the balloon envelope would have to be strong, and therefore heavy, to withstand being held against the wind by the tether.  Even a balloon envelope only three times as thick as those designed for zero-wind conditions would result in no payload capacity at all.
The kite seems the most plausible, but that altitude is well beyond the current record of 5.7 km.  A series of kites along the line can help carry the mass of the tether.
None of these things could be referred to as a "satellite".

Depending on your definition of "unlimited" it is not only already possible but you can (or could) already buy it.
Titan Aerospace introduced the Solara last year. It's a solar powered plane with an expected airborne time of 5 years. Obviously they haven't tested it for 5 years but worst case is that you'd have to land it every couple of years for maintenance. The target market is specifically atmospheric satellite.
They had a web page up where you could order one. Last time I checked their website implied that they had 5 orders. They had a progress indicator of when you can expect to get your plane if you have several million dollars to spend and they said that it takes about a month to build one. When I checked they said the earliest you can expect it was 5 months away.
Unfortunately since Google bought the company the website's been down so there's nothing much on their site. But if you google "Titan Solara" you may see pictures of their plane.
Here's an Arstechnica article about the Solara: http://arstechnica.com/information-technology/2013/08/almost-orbital-solar-powered-drone-offered-as-atmospheric-satellite/
Note: The Solara is designed to loiter around 20km up, not 30km.

Facebook is considering building solar powered communication drones. According to the linked Verge story, they'd hover at 20 km.
I wouldn't call these drones satellites, they're not in orbit. An orbit at that altitude would have a speed of nearly 8 km/s and the period of the orbit would be about an hour and a half. A low altitude orbital sat wouldn't hover stationary over a given location. You need to get up to about 36,000 kilometers before the sats slow down enough to match the earth's rotation.
Edit: adding an illustration to show how altitude affects radius of footprint.

Where r is radius of earth (6378 km) and a is altitude drone (either 20 or 30 km).
Footprint radius for low altitudes is approximated by r sin α where α is acos(r/(r+a))
For a drone at 20 km this comes a radius of 503 km, for a drone at 30 km, this comes to a radius of 616 km. (503/616)^2 is ~.668. Lowering drone to 20 km would give a footprint of about 2/3 the area.

There's yet no name for "an object hovering at XX meters altitude broadcasting TV signals"; anyway such an object is "orbiting" in the sense it is rotating around Earth axis at 1 "round per day", which is around 2000 km/h (but the whole atmosphere moves at same speed, so it appears "geostationary" and also "airstationary"... another non-existing term).

We are all rotating about the earth's axis. By your definition I am in orbit about the earth as I type this reply. Our speed is cos(latitude)2π6378 km/day. At the equator our speed is about 1670 km/hour. At the poles it's 0 km/hr.

Do you type while flying? ;-)

No, never have typed on a plane, I don't fly much. If I were on a westward flight, I'd be moving even slower wrt to earth's center than I am now sitting firmly on the ground.